Side-by-side slotted waveguides coupled to an angularly disposed feed guide



June 1964 A. L. TASHJIAN 3,137,856

SIDE-BY-SIDE SLOTTED WAVEGUIDES COUPLED TO AN ANGULARLY DISPOSED FEED GUIDE 2 Sheets-Sheet 1 Filed NOV. 50, 1961 wig bx o

INVENTOR. ALBERT L. TASHJIAN BY $4, 224a x041 A MPL I TUDE June 1964 A. L. TASHJIAN 3,137,356

SIDE-BY-SIDE SLOTTED WAVEGUIDES COUPLED TO AN ANGULARLY DISPOSED FEED GUIDE Filed Nov. 50, 1961 2 Sheets-Sheet 2 DE GRE E 5 BYWM} Z446. 24

United States Patent 3,137,856 Patented June 16, 1964 3,137,856 SIDE-BY-SIDE SLOTTED WAVEGUIDES COUPLED TO AN ANGULARLY DISPOSED FEED GUIDE Albert L. Tashjian, Brooklyn, N.Y., assignmto Maxson Electronics Corporation, New York, N.Y., a corporation of New York Filed Nov. 30, 1961, Ser. No. 156,042 Claims. (Cl. 34377 1) This invention relates to microwave antennas and particularly to an antenna which provides an improved energy distribution pattern having a narrow directive bearn width and low side lobe level.

Directive high-frequency antenna radiation patterns are generally accompanied by some undesirable side lobe distribution on each side of the main beam width. These side lobes are wasteful of power and tend to cause reflection and otherwise impair the desired operation while serving no useful purpose. In the past it has been difficult to achieve a sufiiciently narrow main beam width pattern while also maintaining side lobes within a limited energy level.

It is, therefore, the primary object of the present invention to provide a novel antenna configuration which achieves a narrow main beam power distribution while minimizing side lobe radiations.

The present device utilizes a novel arrangement of a plurality of adjacent waveguide radiating elements supplied at a constantly changing phase delay by a common feed line. The basic operation of an antenna of this type has been disclosed in prior application Serial No. 798,078, filed March 9, 1959, in the name of Judd Blass, and assigned :to the same assignee as the instant application. Radiating holes at the end of the adjacent waveguide are anti-phased to provide proper power distribution. Coupling holes in directional couplers between each waveguide and the common feed line are arranged in a predetermined pattern to cause a fiat response or uniform output from the full waveguide aperture and a superimposed parabolic wave response from the center portion of the aperture. The resultant of the two patterns effects cancellation of side lobes to form the desired overall power distribution. understood and other objects and advantages will become apparent in the following description and accompanying drawings, which:

FIG. 1 shows a waveguide arrangement as used in the present invention to form a predetermined optimum distribution pattern;

FIG. 2 shows the relation of the two superimposed patterns supplied by the instant novel antenna configuration; and

FIG. 3 diagrammatically shows the cancellation of side lobes and reinforcement of the main beam by the present invention.

As shown in FIG. 1, microwave energy is fed into a main feed line 2 which crosses a plurality of juxtaposed alternately numbered waveguide radiating elements 4 and 6 arranged longitudinally in a common direction. The energy is coupled into the guide in a series arrangement, with the feed line angle causing a constant phase delay between successive elements along the line, which permits directional radiation in a selected area. A directional coupler having holes 8 of a predetermined size at each intersection between the feed line and waveguide, determines the power received by the particular waveguide. The full width of all the individual radiating apertures or openings taken as a unit is designated as It), and a smaller central portion is designated as 12.

In the particular embodiment shown, the lower end of the plurality of waveguides is closed and radiation oc- The invention will be more fully curs from holes 14 in the surface adjacent the end. The holes in each adjacent guide 4 and 6 have an alternately dilferent diagonal pattern so that every other element is anti-phased for proper power distribution. With simple modifications, radiation can also occur from open ends of the guide. The opposite end of each guide is terminated in a load 16, and the feed line having input power entering at one end 18 is terminated at the other end in a load 20.

The desired output pattern of FIG. 2 is obtained by a predetermined arrangement of the coupling holes at the various waveguides. The total aperture of the antenna is considered to extend from '-T to +7, or 27', which is equivalent to the width 10 of FIG. 1, and for convenience will be referred to as L in the equations below. The flat pedestal portion 21 of FIG. 2 represents a uniform output from all the waveguides and the curved portion 23 is in the form of a parabolic wave radiated only from central section 12 of the total aperture. The relation between the pedestal and parabolic curve is not critical and may be adjusted to meet particular beam width and side lobe requirements. The optimum pattern is thus derived from the sum of these two distribution patterns, which permits achieving a narrow beam width for a particular minimum side lobe level.

In the arrangement of FIG. 2, the parabolic curve is radiated from 70% of the total aperture and at peak value represents 6 db added to the pedestal. The distribution is a continuous function over the range from -'r to +7, but includes two points 22, where the ends of the parabolic curve join the flat portion, which represent a discontinuity in the first derivative of the functions. The energy distribution thus ranges from a maximum at the center of section 12 to a minimum at the end 22.

From the principle of superposition, the overall resultant antenna pattern is the sum of the two patterns of uniform distribution and parabolic distribution. Essentially, the theory underlying this type of distribution depends upon the fact that the side lobe levels of the uniform distribution are cancelled by the parabolic distribution, or vice versa.

FIG. 3 shows diagrammatically how the combined distribution effects a resultant side lobe cancellation and a reinforcement of the main beam. In this figure, curve 30 represents the radiation pattern resulting from the uniform amplitude distribution that covers the entire aperture. Curve 32 represents the radiation pattern re sulting from a well. known parabolic distribution equathe central 70% of the total antenna aperture. The uniform amplitude distribution curve 30 results in a sin ,1.

radiation pattern where 0 p X SlIl L(=2T) is the length of the antenna in the plane of the radiation pattern.

A is the wavelength of the operating frequency.

0 is the pattern angle with respect to the normal to the aperture.

The

distribution over 70% of the aperture results in a radiation pattern This result can be verified by direct integration of the Fourier Integral and making the proper conversion to the variable ,u. The resultane radiation pattern, curve 30+curve 32, as a function of ,u. is:

term is shown in FIG. 3 as the curve 30 which is considered the basic narrow beam radiation pattern and sin .7 cl (sin .7,u) i' -7!4 +6113 i represents curve 32, which permits the selection of a desired beam width and side lobe level. The cancellation elfect is thus shown in FIG. 3. The parabolic distribution on the central 70% of the aperture may be replaced by a suitable cosine distribution with very little difference in the radiation pattern, particularly where the side lobe levels are below the main lobe level by a ratio of about 24 db. For larger ratios, the parabolic distribution is preferred by virtue of its inherent higher side lobes. In addition, antennas suitable for various other distribution patterns, such as the Taylor, (cos) (cos) +pedestal, uniform or exponential may be employed. Although the present device is shown having a series feed arrangement, parallel feed may similarly be used.

The present invent-ion therefore provides a novel antenna configuration having an optimum narrow beam width radiation pattern with minimum side lobe level.

While only a single embodiment has been illustrated, it

is apparent that theinvention is not limited to the exact form or use shown and that many variations may be made to the particular design and configuration without departing from the scope of the invention as set forth in the appended claims.

What is claimed is:

1. A microwave energy radiating directional antenna comprising a plurality of juxtaposed waveguides having radiating ends arranged in a common direction, means at said ends to cause said guides to be alternately antiphased, feed line means crossing each said guide at an angle causing a constant phase delay between each subcessive guide, directional coupler means providing predetermined energy coupling from said feed line means into each guide and providing coupling to one group of guides to produce a uniform flat radiation distribution pattern and to a second group of guides where some of the second are part of the first to produce a curved distribution pattern varying from a minimum at the ends of said second group to a maximum at the center, said patterns being additive to produce a narrow main beam with minimum side lobes.

2. The device of claim 1 wherein said ends of said guides comprise radiating holes and said anti-phasing means at said ends includes an alternately different pat tern for said holes on each adjacent guide.

3. The device of claim 2 wherein the end of each said guide opposite said'radiating end is terminated in a load.

4. The device of claim 3 wherein said feed line comprises an input end adapted for connection to a microwave power source and an opposite end terminated in a load.

5. The device of claim '4 wherein said first group of guides comprises the entire plurality of said guides and said second group of guides comprises acentral portion of said plurality of guides.

References Cited in the file of this patent UNITED STATES PATENTS 2,967,301 Rearwin Jan. 3, 1961 FOREIGN PATENTS 855,262 Great Britain Nov. 30, 1960 

1. A MICROWAVE ENERGY RADIATING DIRECTIONAL ANTENNA COMPRISING A PLURALITY OF JUXTAPOSED WAVEGUIDES HAVING RADIATING ENDS ARRANGED IN A COMMON DIRECTION, MEANS AT SAID ENDS TO CAUSE SAID GUIDES TO BE ALTERNATELY ANTIPHASED, FEED LINE MEANS CROSSING EACH SAID GUIDE AT AN ANGLE CAUSING A CONSTANT PHASE DELAY BETWEEN EACH SUCCESSIVE GUIDE, DIRECTIONAL COUPLER MEANS PROVIDING PREDETERMINED ENERGY COUPLING FROM SAID FEED LINE MEANS INTO EACH GUIDE AND PROVIDING COUPLING TO ONE GROUP OF GUIDES TO PRODUCE A UNIFORM FLAT RADIATION DISTRIBUTION PATTERN AND TO A SECOND GROUP OF GUIDES WHERE SOME OF THE SECOND ARE PART OF THE FIRST TO PRODUCE A CURVED DISTRIBUTION PATTERN VARYING FROM A MINIMUM AT THE ENDS OF SAID SECOND GROUP TO A MAXIMUM AT THE CENTER, SAID PATTERNS 